Neutrino is a multiuser operating system; it lets
multiple users log in and use the system simultaneously, and it protects them
from each other through a system of resource ownership and permissions.

Depending on the configuration, your system boots into either
Photon (i.e. graphical) or text mode and prompts you for your user ID and
password.
For more details, see the
Controlling How Neutrino Starts
chapter in this guide.

Your system might have been configured so that you don't have to log in
at all.

When you first install Neutrino, the installation
process automatically creates a single user account called root.
This user can do anything on your system; it has what Windows
calls administrator's privileges.
Unix-style operating systems call root the superuser.

Initially, the root account doesn't have a password.
To protect your system, you should:

Set a secure password for this account as soon as you've installed the OS.

Create a non-root account (see
Managing User Accounts)
to use for your day-to-day work,
to help prevent you from accidentally modifying or deleting system-level
software.

You need to log in as root to do some things, such as starting
drivers, performing system-administration tasks, and profiling
applications.

The default command-line prompt indicates which user ID you're using:

For root, it's a number sign (#).

For other users, it's a dollar sign ($).

For information about changing the prompt, see
“.kshrc”
in the Examples appendix.

If you've configured your system to start Photon, the system automatically
starts
phlogin2 or phlogin
to display a login dialog.
Enter your user name or click your user icon, enter your password, and
then click Login.

If your system is configured to boot into text mode, the
system automatically starts the
login
utility, which prompts you for your user name and then your password.

If you type an invalid user name, the system prompts you for the password
anyway.
This avoids giving clues to anyone who's trying to break into the system.

Text mode on an x86 machine could be on a physical console supplied by
devc-con or devc-con-hid.
On any other type of machine, you could be connecting to the target via a
serial port or TCP/IP connection.

After you've logged in, the system automatically runs the
/home/username/.profile script.
This script lets you customize your working environment without affecting
other users.
For more information, see
Configuring Your Environment.

Enter
login
at the command prompt, and then enter the user's name and password.

The su
(switch user ID) utility also lets you run as another user, but temporarily.
It doesn't run the user's profiles or significantly modify the environment.
For more information, see the Utilities Reference.

Select Log Out from the Launch or Desktop menu, or enter
phshutdown
on the command line.
The shutdown dialog appears.

Select Logout (End Photon session) and click Ok.
If your system is configured to start Photon, the
phlogin2 or phlogin
dialog reappears.
If you started Photon manually from text mode, the system returns to text
mode.

Even if your system started Photon automatically, you can exit your Photon
session and run in text mode.

To switch from Photon to text mode:

In the login dialog, click Shutdown.
The shutdown dialog appears.

Enable Exit to text mode and click Ok.

If you start a terminal session from within Photon — for example,
by clicking Terminal on the shelf — the
pterm
utility starts a shell that runs as the current Photon user.
You can log in and out as a different user, just as in text mode, but when you
log out, the pterm window closes.

You rarely need to reboot a Neutrino system.
If a driver or other system process crashes, you can usually restart that
one process.

Don't simply turn off a running Neutrino system, because processes
might not shut down properly, and any data that's in a filesystem's cache
might not get written to the disk.
For information about reducing this effect, see
“Filesystems and block I/O (devb-*) drivers”
in the Fine-Tuning Your System chapter.

To shut down or reboot the system in text mode, use the
shutdown
command.
You can do this only if you're logged in as root.
This utility has several options that let you:

name the node to shut down (default is the current node)

specify the type of shutdown (default is to reboot)

shut down quickly

list the actions taken while shutting down (i.e. be verbose)

In Photon, you can run
phshutdown
from the command line, or choose Shutdown from the Launch or Desktop menu.
By default, you don't have to be root to do this.

Before shutdown and phshutdown shut down the system,
they send a SIGTERM signal to any running
processes, to give them the opportunity to terminate cleanly.
For more information on these utilities, see
in the Utilities Reference.